In wireless communications involving artificial satellites, a circular polarized antenna with near omni-directional coverage is generally required such that the link is not interrupted by mobility at either end of the communications link. For simultaneous two-way communications, two separate communication channels or frequency bands are used. The electromagnetic frequency spectrum used for this purpose generally falls within the range of 700 megahertz (MHz) through 7500 MHz. In one such application for commercial purposes, the transmit band for terrestrial terminals is 1626.5 MHz through 1660.5 MHz and the receive band is 1525 MHz through 1559 MHz.
A quadrifilar helix antenna (QHA) is capable of performing these communication functions for hand-held terminals. In order for optimum power transfer to take place through the antenna, such antennas operate at resonance for both the channels (i.e., receive and transmit).
The QHA typically includes an array of monopoles twisted into a helical structure and connected by a non-radiating feed structure to excite the desired sense of circular polarization of the desired sense (right handed or left handed). The antenna is constricted with less than a full turn such that the radiation pattern of the antenna becomes substantially omni-directional without any null occurring in the communication space. This condition is generally known as the normal mode of operation of the helical antenna. The antenna elements are generally constructed as printed conducting strips on a thin dielectric substrate. The frequency bands for communication determines the resonant length of the antenna elements and hence the antenna height, whereas the radiation pattern or antenna gain requirements determine the diameter to height ratio in terms of the operating central frequency of the band.
Convenience and ease of operation creates the need to miniaturize the antenna such that the individual consumer can easily carry the hand-held terminal. Wireless signals transmitted directly from a satellite may not be strong enough to penetrate walls to reach a person inside a building or operating in a city area with high rise building. However, a hybrid system generally known in the industry as Mobile Satellite Services (MSS) with Ancillary Terrestrial Components (ATC) overcomes this shortcoming by using satellites integrally with terrestrial cellular wireless communication networks. This advancement in mobile wireless communication technology has created a consumer demand to have hand-held satellite-cellular terminals that are thinner and smaller.
For the frequency bands of mobile wireless communications in the frequency range of 1000 MHz through 3000 MHz, the regular QHAs for the transmit and the receive bands are about the size of a cigar. For example, the QHA may have a length of approximately six to seven inches and diameter of about 0.75 inches.